Pointrow mentioned above using Dawn detergent to clean glasses. I used to use Dawn. My eye doctor told me the Dawn was ruining the coatings on my eyeglasses.  So, now I use a glass cleaner that I buy at the local Rite Aid.  I always run water over them before using the lens cleaner, to wash off the dust, etc.

Do you have multiple pairs of glasses? If not, have you thought about buying at least 2 pairs when you buy them.  Use one pair when you are in situations on the farm where you expect they can get scratched. Keep the other pair for at home, when you want to keep them for reading, etc.  Just a thought.